Weight Distribution
- Thread starter ABEJR2004
- Start date
Tennesseahawk
Veteran Expediter
Just talked to a friend today about his Volvo t/t. He says he's over when empty, and the scales don't bother him. It's a common problem. With you, however, I would imagine you'd be pulled in a few times; just cause you're driving something a bit outta the ordinary.
Are you planning on putting another axle on the beast?
bdmj989900
Seasoned Expediter
Not planning on it. Maybe in the future. Just had apu put on. The sticker on the door shows 12000 for the front. Was close to that but the apu made it go over. They put it as far to the back as they could. When load i put everything over the center of the rear axle Painted a white line on the floor so i know where its at.
DocRushing
Expert Expediter
Marda and I own and run a 2006 Freightliner Columbia with a 90-inch sleeper and a 22-foot cargo box.
With full fuel tanks and a full complement of our personal gear, even with no cargo, the front axle bears slightly over 12,000 pounds.
Fortunately, the front axle is rated at 12,500 pounds.
No law-enforcement technician has ever given us any grief about the weight on the front axle.
If I were writing the specs for another truck, I'd shorten the wheelbase by nine inches -- to shift about 360 pounds from the front axle onto the rear.
Because of the nose-heaviness of our truck, when we load cargo, we must carefully avoid adding more weight onto the front axle.
That is, we must carefully avoid loading the cargo in such a way that the center of mass of the cargo rests anywhere forward of the rear axles.
Usually I prefer to place the center of mass of the cargo slightly behind the effective centerline of the rear axles -- to shift about 500-800 pounds from the front axle onto the rear -- to improve the ride and the handling -- and to reduce the wear of the front tires.
Sooo -- how far behind the rear axles should I place the cargo?
That depends.
It depends on how much weight I wish to transfer, and how much the cargo weighs.
That leads me to a simple calculation.
Here's how -- in an explanation which I first posted in September 2004.
By the way, I've successfully used this technique for loading and ballasting not only trucks and buses but also aircraft, submarines, and surface ships -- since 1961.
Here 'tis:
This principle is very useful in loading a truck:
If the driver loads the cargo in such a way that the center of mass (center of gravity) is directly above the drive axle (or halfway between the tandem drive axles), then the entire weight of the cargo bears directly onto the drive axle(s).
If the driver loads the cargo in such a way that the center of mass is somewhere forward of the drive axle(s), then some of the weight bears onto the steering axle, and less of the weight bears onto the drive axle(s).
The farther the center of mass of the cargo is forward of the drive axle(s), then the more of the weight bears onto the steering axle.
Conversely, if the driver loads the cargo in such a way that the center of mass is behind the drive axle(s), then all of the weight of the cargo bears onto the drive axle(s) -- and some of the weight on the steering axle shifts onto the drive axle(s)!
The farther the center of mass of the cargo behind the drive axle(s), the more of the weight on the steering axle shifts onto the drive axle(s).
How much weight goes on or comes off the steering axle?
That's easy -- with a simple calculation:
If the center of mass of the cargo is 5 feet forward of the drive axle(s) or behind the drive axle(s), and if the wheelbase is 25 feet, then 5/25 of the weight moves.
5/25 = 1/5 = 0.20 = 20%.
In this same example, if the cargo weighs 5,000 pounds, then 1,000 pounds (1/5 of 5,000 pounds) shifts onto the steering axle or off it -- depending on whether the center of mass of the cargo is 5 feet forward of the drive axle(s) or 5 feet behind the drive axle(s).
If the center of mass of the cargo is 5 feet forward of the drive axle(s), then 1,000 pounds of the cargo bears onto the steering axle, and 4,000 pounds bears onto the drive axle(s).
In the other direction, if the center of mass of the cargo is 5 feet behind the drive axle(s), then all 5,000 pounds comes to bear on the drive axle(s) -- AND 1,000 pounds come off the steering axle and shift onto the drive axle(s), so that 6,000 pounds altogether come to bear onto the drive axle(s).
To picture this, imagine a seesaw on a playground.
Imagine what happens -- imagine the action of the seesaw -- as two or more children take different positions on the seesaw.
Now imagine that your truck is a seesaw with its fulcrum at the drive axle(s).
Then imagine what happens as your cargo occupies different positions -- fore and aft -- inside your cargo box.
This is not empty speculation; it really works.
Note this well:
If a driver wishes to avoid adding more weight to the steering axle, load the cargo in such a way that the center of mass of the cargo is nowhere forward of the drive axle(s) -- either directly above the drive axle(s) or behind the drive axle(s).
How can we determine where the center of mass is?
A careful eyeball estimate often works fairly well.
Maybe we could even measure the cargo.
Try this sometime!
By the way, this principle is one very good reason to avoid loading cargo all the way into the nose of the cargo box unless necessary.
Many loaders tend to shove the cargo all the way into the nose -- even if the cargo is rather small.
Many drivers also tend to do so.
By controlling the position of the cargo, we can control not only the loading of the axles but also the quality of the ride and the handling of the truck.
As always, best wishes to all,
Doc.
PS. For those who dislike math and physics, please feel free to disregard this whole thing.
Again, best wishes to all,
Doc.
With full fuel tanks and a full complement of our personal gear, even with no cargo, the front axle bears slightly over 12,000 pounds.
Fortunately, the front axle is rated at 12,500 pounds.
No law-enforcement technician has ever given us any grief about the weight on the front axle.
If I were writing the specs for another truck, I'd shorten the wheelbase by nine inches -- to shift about 360 pounds from the front axle onto the rear.
Because of the nose-heaviness of our truck, when we load cargo, we must carefully avoid adding more weight onto the front axle.
That is, we must carefully avoid loading the cargo in such a way that the center of mass of the cargo rests anywhere forward of the rear axles.
Usually I prefer to place the center of mass of the cargo slightly behind the effective centerline of the rear axles -- to shift about 500-800 pounds from the front axle onto the rear -- to improve the ride and the handling -- and to reduce the wear of the front tires.
Sooo -- how far behind the rear axles should I place the cargo?
That depends.
It depends on how much weight I wish to transfer, and how much the cargo weighs.
That leads me to a simple calculation.
Here's how -- in an explanation which I first posted in September 2004.
By the way, I've successfully used this technique for loading and ballasting not only trucks and buses but also aircraft, submarines, and surface ships -- since 1961.
Here 'tis:
This principle is very useful in loading a truck:
If the driver loads the cargo in such a way that the center of mass (center of gravity) is directly above the drive axle (or halfway between the tandem drive axles), then the entire weight of the cargo bears directly onto the drive axle(s).
If the driver loads the cargo in such a way that the center of mass is somewhere forward of the drive axle(s), then some of the weight bears onto the steering axle, and less of the weight bears onto the drive axle(s).
The farther the center of mass of the cargo is forward of the drive axle(s), then the more of the weight bears onto the steering axle.
Conversely, if the driver loads the cargo in such a way that the center of mass is behind the drive axle(s), then all of the weight of the cargo bears onto the drive axle(s) -- and some of the weight on the steering axle shifts onto the drive axle(s)!
The farther the center of mass of the cargo behind the drive axle(s), the more of the weight on the steering axle shifts onto the drive axle(s).
How much weight goes on or comes off the steering axle?
That's easy -- with a simple calculation:
If the center of mass of the cargo is 5 feet forward of the drive axle(s) or behind the drive axle(s), and if the wheelbase is 25 feet, then 5/25 of the weight moves.
5/25 = 1/5 = 0.20 = 20%.
In this same example, if the cargo weighs 5,000 pounds, then 1,000 pounds (1/5 of 5,000 pounds) shifts onto the steering axle or off it -- depending on whether the center of mass of the cargo is 5 feet forward of the drive axle(s) or 5 feet behind the drive axle(s).
If the center of mass of the cargo is 5 feet forward of the drive axle(s), then 1,000 pounds of the cargo bears onto the steering axle, and 4,000 pounds bears onto the drive axle(s).
In the other direction, if the center of mass of the cargo is 5 feet behind the drive axle(s), then all 5,000 pounds comes to bear on the drive axle(s) -- AND 1,000 pounds come off the steering axle and shift onto the drive axle(s), so that 6,000 pounds altogether come to bear onto the drive axle(s).
To picture this, imagine a seesaw on a playground.
Imagine what happens -- imagine the action of the seesaw -- as two or more children take different positions on the seesaw.
Now imagine that your truck is a seesaw with its fulcrum at the drive axle(s).
Then imagine what happens as your cargo occupies different positions -- fore and aft -- inside your cargo box.
This is not empty speculation; it really works.
Note this well:
If a driver wishes to avoid adding more weight to the steering axle, load the cargo in such a way that the center of mass of the cargo is nowhere forward of the drive axle(s) -- either directly above the drive axle(s) or behind the drive axle(s).
How can we determine where the center of mass is?
A careful eyeball estimate often works fairly well.
Maybe we could even measure the cargo.
Try this sometime!
By the way, this principle is one very good reason to avoid loading cargo all the way into the nose of the cargo box unless necessary.
Many loaders tend to shove the cargo all the way into the nose -- even if the cargo is rather small.
Many drivers also tend to do so.
By controlling the position of the cargo, we can control not only the loading of the axles but also the quality of the ride and the handling of the truck.
As always, best wishes to all,
Doc.
PS. For those who dislike math and physics, please feel free to disregard this whole thing.
Again, best wishes to all,
Doc.
Good to see ya in here Doc, hope you guys are doin ok!!
We are nose heavy and load all loads by the teeter tooter rule as well. We run with our lift axle down way more than most, for the same reason. We did have a problem a while back being overweight on the front, wrong size tires.
We are nose heavy and load all loads by the teeter tooter rule as well. We run with our lift axle down way more than most, for the same reason. We did have a problem a while back being overweight on the front, wrong size tires.